Concatenated motor assembly

ABSTRACT

A concatenated motor assembly for providing rotational power that includes a continuous rotatable shaft cooperating with a first motor module assembly. The first motor module assembly communicates with a motor coupling unit, which in turn communicates with a second motor module. The second motor module and the motor coupling unit each cooperate with the rotatable shaft. The first and second motor modules are wound rotor electric motor. The first motor module assembly generates and provides an induced current to the motor coupling unit, which in turn provides power input to the second motor module assembly.

RELATED APPLICATIONS

This application is a divisional application of U.S. Non-ProvisionalApplication Ser. No. 09/621,206 filed Jul. 21, 2000 now U.S. Pat. No.6,468,058, and claims the benefit of U.S. Provisional Application Ser.No. 60/144,967 filed Jul. 21, 1999.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to the field of motors, and moreparticularly but not by way of limitation, to a concatenated motorassembly that includes a first stator inducing a current in a rotoradjacent the first stator for use in powering a second stator.

2. Discussion

A variety of systems are used to bring fluids from below ground to thesurface in a well when the pressure is insufficient or it is beneficialfor other reasons. One common method involves using a pumping system todraw fluids from the producing formation(s) to the surface forcollection and processing. In one class of pumping systems, asubmersible pumping unit is immersed in the well-bore fluids and drivento force fluids through production tubing to the earth's surface. Suchpumping systems typically include an electric submersible motor (ESM), asubmersible production pump with sealing portions to protect the motorfrom well-bore fluids, a gearbox, and a variety of other controls suchas a variable speed drive (VSD).

In many pumping systems, centrifugal pumps are used but centrifugalpumps are not adequate in a number of circumstances. In particular,centrifugal pumps are typically inefficient at lower pump speeds.Alternatives to centrifugal pumping systems include positivedisplacement pumping systems, such as a progressive cavity pumpingsystems (PCS). During the start-up phase of the pumping system a highertorque is needed from a motor portion of the pumping system to drive theprogressive pump portion of the pumping system. In order to provide thehigher torque required at start-up, and to speed match the motor to theoperating range of the progressive cavity pump portion of the system,the progressive cavity pumping system usually includes a gear reducerfor increasing motor output torque and speed matching.

Typically, such gear reducers are positioned within the well-bore andthus are size constrained. Also, such gear reducers operate at speedsdetermined by a fixed ratio of the output speed of the motor, so motorsof the progressive cavity pumping system generally need to be coupledwith a variable speed driver to effect operation of the prior artprogressive cavity pumping system over a range of speeds. Even when avariable speed drive is used, the gear reducers limit the range ofspeeds for operating the progressive cavity pump portion of aprogressive pumping system, typically making higher production ratesunavailable. Thus prior art progressive cavity pumping systemsordinarily fail to afford the flexibility necessary to pump fluids atboth low and high flow rates.

Within a typical prior art progressive cavity pumping system, a motorcoupled to a variable speed drive exhibits decreasing torque in responseto an input from the variable speed drive for a lower rotational speedand show significant decreases in available torque for current suppliedat frequencies below 30 Hertz. Additionally, the maximum torque transferof a gearbox assembly within a typical prior art progressive cavitypumping system is limited by the gearbox size, specifically an availablediameter for the gears of the gearbox; thus a well-bore diameter oftenlimits the available horsepower of a typical prior art progressivecavity pumping system. Within a typical well-bore, the availablehorsepower of most progressive cavity pumping systems equipped with agearbox and operating under a variable speed drive is limited to about80 horsepower. Furthermore, the inclusion of a gearbox and a variablespeed drive in a prior art progressive cavity pumping system addsignificantly to the cost of the system.

Variable speed drives (VSD) are often used in conjunction with a gearboxwithin a prior art progressive cavity pumping system to achieve a wideroperating speed range but an alternative method is to use the VSDdirectly with an ESM to run the motor in a controlled low speedoperation. However, a prior art progressive cavity pumping system with avariable speed drive coupled directly to a motor of the system typicallyhas a limiting starting torque, which often proves to be insufficientfor a system utilizing a progressive cavity pump that requires astarting torque of nearly 145% of the running torque of the system.Also, a prior art progressive cavity pumping system configured with avariable speed drive coupled directly to an electric submersible motoris horsepower limited and non-applicable to a number of submersibleapplications.

Therefore, challenges remain and a need persists for a cost competitive,progressive cavity pumping system compliant with high torque start-updemands placed on the system, while providing improved reliability forsteady state operation of the pumping system.

SUMMARY OF INVENTION

A concatenated motor assembly includes a continuous rotatable shaft, afirst motor module assembly, a motor coupling unit, and a second motormodule assembly. The first motor module assembly cooperates with thecontinuous rotatable shaft and provides an induced current whilerotating the continuous rotatable shaft. The motor coupling unitcooperates with the continuous rotatable shaft, communicates with thefirst motor module assembly, receives the induced current and providespower. The second motor module assembly communicates with the motorcoupling unit, cooperates with the continuous shaft and uses theprovided power to further rotate the continuous shaft.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side elevational diagram, in partial cross-section, of anoil well having disposed therein an electrical submersible pumpingsystem driven by a concatenated motor system constructed in accordancewith the present invention.

FIG. 2 is a longitudinal cross section of the concatenated motorassembly of FIG. 1.

FIG. 3 is a longitudinal cross section, cutaway view of one of the motorassemblies of FIG. 1.

FIG. 4 is an enlarged cross section of a portion of the motor of FIG. 3.

FIG. 5 is a cutaway view of the motor coupling unit of FIG. 2.

FIG. 6 is a schematic diagram of the electrical motor circuit showingthe connections between the two motors of the concatenated motorassembly of FIG. 1.

FIG. 7 is a graph of typical, actual torque versus motor speed for atypical progressive cavity pump.

FIG. 8 is a flow chart of the sequence of operation of the electricalsubmersible pumping system depicted in FIG. 1.

DESCRIPTION

For purposes of disclosure and convenience of enablement, a pump systemusage environment has been elected to aid in the understanding andpresentation of the present invention and does not constitute alimitation on the uses of the present invention for alternate uses.Referring to the drawings in general and particularly to FIG. 1,depicted therein is a submersible concatenated pump system 10constructed in accordance with the present invention. While the presentinvention will be described in relation to the embodiment shown in theappended drawings, it will be understood that the present invention canbe adapted to other embodiments.

The concatenated pump system 10 is connected to a production tubingstring 11 and supported thereby in a well-bore 12 and includes a powersupply 13 supplying power through a power cable 14 to a concatenatedmotor assembly 15 used to drive a pump assembly 16. The pump assembly 16includes a pump 17 and a seal assembly 18 attached to the concatenatedmotor assembly 15. The concatenated motor assembly 15 has a primary orcontrol concatenation unit 20 and a secondary concatenation unit 22.

As shown by FIG. 2, the primary concatenation unit 20 comprises a firstmotor module assembly 24 connected to a motor coupling unit 26, whilethe secondary concatenation unit 22 includes a second motor moduleassembly 28 coupled to the motor coupling unit 26. Optionally, thecoupling unit 26 may be integrated with and made part of the first motormodule assembly 24. In either case, the coupling unit 26 provides boththe mechanical and the electrical connection between the primaryconcatenation unit 20 and the secondary concatenation unit 22. For theparts that are similar between the motor module assembly 24, thecoupling unit 26 and the motor module assembly 28, the numberingconvention will be designated by a common numeric character accompaniedby the alpha character ‘A’ for the first motor module 24, the alphacharacter ‘B’ for the second motor module 28, and the alpha character‘C’ for the motor coupling unit 26. In a preferred embodiment, the powersupply 13 (of FIG. 1) supplies power to the primary concatenation unit20 via the power cable 14 to a first power connection 30A forapplication to the first motor module 24.

Shown in greater detail by FIG. 3, the first motor module assembly 24includes an elongated motor housing 32A forming a first central bore 33A(second central bore 33B in the second motor module assembly 28) andenclosing a wound rotor induction motor 34A. The wound rotor inductionmotor 34A includes a stator portion 36A adjacent the elongated motorhousing 32A and a rotatable wound rotor portion 38A adjacent the statorportion 36A. A rotatable shaft section 40A is supported by a pair offirst bearing assemblies 42A, which in turn supports the wound rotorportion 38A. The pair of first bearing assemblies 42A (second bearingassemblies 42B in the second motor assembly 28) are secured in place bythe elongated housing 32A. The rotatable shaft section 40A includes afirst spline 44A for use in linking the first motor module assembly 24to the coupling unit 26 and a second spline 46A for use in linking theconcatenated motor assembly 15 to additional concatenated motorassemblies of alternate embodiments.

In a preferred embodiment, the wound rotor induction motor 34A is athree phase induction motor. As such, the stator portion 36A is a threephase, Y-connected motor with three pairs of windings spaced 120° apart(not shown separately) that respond to applied voltages that have a120-degree phase displacement. Applying three-phase power to thewindings of the stator portion 36A sets up a rotating magnetic field.Similar to the stator portion 36A, the wound rotor portion 38A has threepairs of Y-connected windings spaced 120° complimentary to the threepair of windings of the stator portion 36A. The rotating magnetic fieldof the stator portion 36A induces a magnetic field in the wound rotorportion 38A by cutting through the three pairs of Y-connected windingsresulting in an induced electromagnetic force (emf). The two fieldsinteract and cause the wound rotor portion 38A to turn in the directionof the rotating magnetic field of the stator portion 36A and relative tothe elongated motor housing 32A. The current developed in the windingsof wound rotor portion 38A of the induction motor 34A is passed to thecoupling unit 26, which collects the current and provides power to astator portion 36B of a second induction motor 34B as shown in FIG. 2.The frequency of the three phase power supplied to the second inductionmotor 34B is determined by the frequency of the power supplied to thefirst induction motor 34A and the rotational speed of the wound rotorportion 38A relative to the stator portion 36A.

Returning to FIG. 2, the coupling unit 26 includes a rotatable shaftsection 40C with a first spline 44C and a second spline 46C while thesecond motor module 28 includes a rotatable shaft section 40B with afirst spline 44B and a second spline 46B. Collectively, the rotatableshaft sections 40A, 40B and 40C combine to form a continuous rotatableshaft 49 via a coupling between their respective splines, i.e., spline44A coupled with spline 46C, and spline 44C coupled with spline 46B.

The wound rotor induction motor 34A, a portion of which is shown in FIG.4, has the cylindrically shaped rotor portion 38A attached to thecontinuous rotatable shaft 49 of the concatenated pump system 10, whichrotates within the cylindrically shaped stator portion 36A. The rotorportion 38A is made up of a series of rotor segments 50A separated byoil bearings 52A. The stator portion 36A is made up of steel laminations54A and brass laminations 56A including a series of stator windings 58Arunning through the laminations that are coupled to the power conductor30A, causing rotation of the rotor portion 38A within the wound rotorinduction motor 34A, in a manner well known in the art. As will beappreciated by those skilled in the art, stator windings 58A willtypically be wound and connected in groups depending upon the design ofthe stator portion 36A, the number of poles in the wound rotor inductionmotor 34A, and the desired speed of the wound rotor induction motor 34A.

In a preferred embodiment the second motor module 28 has substantiallythe same construction as the first motor module 24 described above.However, the second motor module 28 having substantially the sameconstruction as the first motor module 24 is not a limitation on thescope of the invention. Dissimilar construction of the second motormodule 28 relative to the first motor module 24, for example aninduction motor absent a wound rotor portion, is embodied within thescope of the present invention.

The concatenated pump system 10 has the motor coupling unit 26, shown inFIG. 5, which along with the first motor module assembly 24 forms thecontrol concatenation unit 20, as shown in FIG. 2. The motor couplingunit 26 includes bearings 64 disposed between the rotatable shaftsections 40C of the continuous rotatable shaft 49 and an elongatedcoupling housing 70. Included in the motor coupling unit 26 is a portionreferred to as slips 72. The slips 72, as shown in FIG. 5, have twoparts: the stationary outer slips (stator) 74 serve to collect thecurrent developed in the windings of the wound rotor portion 38A of theinduction motor 34A, and to provide the collected current as power tothe stator portion 36B of the second induction motor 34B; inner slips(rotor) 76 rotate within the outer slips 74 and serve to receive thecurrent developed in the windings of the wound rotor portion 38A of theinduction motor 34A.

In a preferred embodiment, the slips 72 have a construction similar tothe induction motor 34A wherein the inner slips 76 are built in a mannersimilar to the rotor portion 38A and the outer slips 74 are built in amanner similar to that of the stator portion 36A, including a series ofwindings running through the outer slips 74, in a manner well known inthe art. As will be appreciated by those skilled in the art, thesewindings will typically be wound and connected in groups depending uponthe design of the motor coupling unit 26.

The inner slips 76 are supported by the continuous rotatable shaft 49,and the inner slips 76 rotate at the same rotational velocity as thewound rotor portion 38A of the induction motor 34A during operation ofthe concatenated pump system 10. The outer slips 74 are connected to thesecond motor module 28 through a connector 78. The inner slips 76 rotatepast the outer slips 74 at a slip ring connector 82.

FIG. 6 is a schematic of a preferred embodiment of the concatenatedmotor assembly 15. The stator portion 36A of the induction motor 34Ashows that windings 84A are three phase, Y-connected pairs of windingsspaced 120 degrees apart. The windings 84A are responsive to appliedvoltages that have a 120-degree phase displacement. Likewise, the rotorportion 38A of the induction motor 34A shows that windings 86A are threephase, Y-connected pairs of windings spaced 120 degrees apart. Thewindings 86A respond to a rotating magnetic field, developed whencurrent is applied to the stator portion 36A of the induction motor 34A.The response of the windings 86A to the rotating magnetic field cuttingthrough the windings 86A is to generate a current. The current generatedhas a frequency offset from the frequency of the current supplied to thestator portion 36A, is modulated by the rotational speed of thecontinuous rotatable shaft 49, and has a voltage phase substantially thesame, with a slight time shift, as the phase of the voltage supplied tothe stator portion 36A.

The first rotor portion 38A is mechanically connected to the inner slips76 via the continuous rotatable shaft 49. The rotation of the innerslips 76 relative to the outer slips 74 induces a power output from theslips 72 used to power stator windings 84B of induction motor 34B of thesecond motor module 28 that is frequency dependent on the rotationalspeed of the continuous rotatable shaft 49. This use of concatenationcreates the concatenated motor assembly 15 displaying a resultant “thirdmotor” response which can have properties different from each individualinduction motor, such as 34A and 34B. The resultant third motor responseof the concatenated motor assembly 15, for instance, can achieve theeffect of additional poles for the concatenated pump system 10, thusallowing the concatenated motor assembly 15 to achieve the equivalent ofa larger number of poles than is physically present in the individualinduction motors, such as 34A and 34B.

The operation of the concatenated pump system 10 will be described withreference to FIGS. 6 through 8. As described above, a concatenated pumpsystem 10 is formed when the shafts of two or more motors are connectedin series to form the continuous rotatable shaft 49 as shown in FIG. 6.In the present concatenated motor assembly 15, the variable speedresults from the unique use of slips 72 and resultant change infrequency applied to the second motor module 28. This change results inthe system taking on different performance characteristics than any ofthe individual motor modules of the originally designed unit. Theresultant speed of the concatenated motor assembly 15 is inverselyproportional to the sum or difference of the number of poles in theconcatenated motors. If the synchronous speed of a two pole motor is3600 rpm on 60 hertz (Hz) power, then the synchronous speed of a fourpole motor is 1800 rpm. The speed of an eight pole motor is 900 rpm, andthe speed of a twelve pole motor is 600 rpm. If the concatenated motorsystem has two motors and one has four poles and the other has eightpoles, the resultant “third motor” or concatenated motor assembly 15could run at 1800 rpm (4+0) or 900 rpm (8+0) or 600 rpm (8+4). It couldalso run in the reverse direction at a speed of 1800 rpm (8−4).

This effectively allows different pole configurations and differentwindings to be combined in the same concatenated pump system 10 by usingthe resultant slip of the slips 72 in the motor coupling unit 26. Thisis preferable because the effective speeds and resultant torque that canbe obtained using concatenated motor assembly 15 are sufficient to powera progressive cavity pump, at the higher horsepower and torquesrequired, absent the use of a gearbox.

The progressive cavity (PC) pump 17, as shown in FIG. 1, is connected tothe second motor module 28 via the seal assembly 18. The second motormodule 28 is in turn connected to the first motor module 24 via themotor coupling unit 26. The first motor module 24 and the motor couplingunit 26 collectively form the control concatenation unit 20. The outputresponse of the first motor module 24 coupled to the second motor module28 via the motor coupling unit 26 work together to produce the resultantequivalent “third motor” discussed above. If the concatenated motorassembly 15 for the PC pump 17 has two motors with a synchronous speedof 3600 rpm on 60 hertz (Hz), one motor with twelve poles and the otherwith eight poles, then the resultant equivalent “third motor” could runat a slow speed of 360 rpm (8+12 poles) with high torque or at a fasterspeed with low torque such as 600 rpm (12+0 poles) or 900 rpm (8+0poles). These are speeds within the range of those shown in FIG. 7,which are those for a typical PC pump, such as PC pump 17.

FIG. 7 shows a curve 90 of torque as a percentage of full load versusmotor speed for a typical progressive cavity (PC) pump. On the y-axis 92is plotted the torque as a percentage of full load and on the x-axis 94is plotted the corresponding motor speed (rpm). These speeds typicallyrange from 100 to 800 rpm for the PC pump and require high initialtorques. At start-up the torque can be nearly 145% of the running torqueas shown at 96. In contrast, the torque at 100 rpm is typically muchlower as shown at 98. The concatenated motor assembly 15 can operate atthese speeds and torques with a particular combination of motors in thecontrol concatenation unit 20 and the secondary concatenation unit 22 asdescribed above.

The operation of the concatenated pump system 10 can be furtherunderstood with reference to FIG. 8, which is a flow chart of the stepsnecessary to pump fluids using the concatenated pump system 10. Itshould be noted that, in general, this is a submersible system but itcould be used as a surface system, or a combination of both. It shouldalso be noted that the diagrams imply a vertically disposed well-borebut in most circumstances the well-bore will have an incline. As shownin FIG. 1, the motor module assembly 28 of the secondary concatenationunit 22 rotates the combined continuous rotatable shaft 49 that rotatesthe pump 17, such as a progressive cavity pump, and moves producedfluids 100, such as oil and gas, from the producing formation via thepump 17 to the surface. The rotational speed of the continuous rotatableshaft 49 is influenced by the control concatenation unit 20 through themotor coupling unit 26.

Referring to FIG. 8, starting with fluids 100 in the well-bore ready tobe pumped to the surface, as shown by step 200, the wound rotorinduction motor 34A of the control concatenation unit 20 is energized bythe power cable 14 through power connection 30A (step 202), the woundrotor induction motor 34A rotates the continuous rotatable shaft 49 ofthe motor coupling unit 26 (step 204). At step 206, the directmechanical linkage from the first wound rotor induction motor 34A drivesthe inner slips (rotor) 76, thereby creating an electromagnetic couplingto the outer slips (stator) 74. As shown in step 208, the output fromthe slips 72 provides the power input to the stator 36B of the secondinduction motor 34B; thus the two induction motors 34A and 34B exhibitproperties of a resultant equivalent third motor as described above,thus powering the pump 17 at the appropriate speed to operate withoutadditional controls. At step 210, fluids 100 enter the pump 17. At step212, the pump 17 energizes the fluids 100; and at step 214, the fluids100 are pumped to the surface.

The present invention is well adapted to attain the ends and advantagesmentioned as well as those inherent therein. While a presently preferredembodiment has been described for purposes of this disclosure, numerouschanges may be made which will readily suggest themselves to one skilledin the art and which are encompassed in the spirit of the inventiondisclosed and as defined in the appended claims.

1. A concatenated motor assembly comprising: a first stator inducing acurrent in an adjacent first wound rotor, wherein the first wound rotorcooperates with a continuous shaft, and the shaft further communicateswith a second wound rotor, the first stator and the first rotor forminga portion of a first motor module assembly, the first motor moduleassembly further having a first elongated housing forming a firstcentral bore supporting a first power connection while confining a firstmotor having a first bearing assembly contiguous to the first centralbore supporting the continuous rotatable shaft, the continuous rotatableshaft attached to the first rotatable rotor encompassed by the firststator restrained within the first bore of the first elongated housing,the first motor module assembly generating the induced current whilerotating the continuous rotatable shaft; and a motor coupling unitresponsive to the current induced in the first wound rotor providingpower to a second stator that is adjacent the second wound rotor.
 2. Theconcatenated motor assembly of claim 1, in which the second stator andthe second rotor form a portion of a second motor module assembly. 3.The concatenated motor assembly of claim 2, wherein the second motormodule assembly further comprises a second elongated housing forming asecond central bore supporting a second power connection while confininga second motor having a second bearing assembly contiguous the secondcentral bore supporting the continuous rotatable shaft, the continuousrotatable shaft attached to the second rotatable rotor encompassed bythe second stator restrained within the second bore of the secondelongated housing, the second motor module assembly electricallyconnected to the motor coupling unit consuming the provided power tofurther rotate the continuous shaft.
 4. The concatenated motor assemblyof claim 3, in which rotatable inner slips cooperate with fixed outerslips to form a portion of the motor coupling unit.
 5. The concatenatedmotor assembly of claim 4, wherein the motor coupling unit furthercomprises an elongated housing supporting a slip connector andsupporting the continuous rotatable shaft, the continuous rotatableshaft attached to the rotatable inner slips encompassed by the fixedouter slips restrained within the elongated housing, the slip connectorconnecting a power connection to the inner slips, the motor couplingunit coupled to the first motor module assembly providing power inresponse to the induced current.
 6. The concatenated motor assembly ofclaim 5, in which the first motor module comprises a number of firstpoles, the second motor module comprises a number of second poles and inwhich the number of first poles differs from the number of second poles.7. The concatenated motor assembly of claim 6, in which the first motormodule comprises at least one motor.
 8. The concatenated motor assemblyof claim 7, in which the second motor module comprises at least onemotor.
 9. The concatenated motor assembly of claim 8, wherein thegenerated induced current is electrical power derived from rotation ofthe first motor module assembly, and wherein the derived electricalpower is the provided power consumed by the second motor module assemblyto further rotate the continuous shaft.
 10. A concatenated motorassembly comprising: a continuous rotatable shaft; a first motor moduleassembly cooperating with the continuous rotatable shaft providing aninduced current while rotating the continuous rotatable shaft; a motorcoupling unit cooperating with the continuous rotatable shaft whilecommunicating with the first motor module assembly receiving the inducedcurrent and providing power; and a second motor module assemblycommunicating with the motor coupling unit while cooperating with thecontinuous rotatable shaft using the provided power to further rotatethe continuous shaft.
 11. The concatenated motor assembly of claim 10,in which the continuous rotatable shaft further cooperating with a pumpassembly.
 12. The concatenated motor assembly of claim 11, in which thepump assembly comprises a pump communicating with a seal assembly. 13.The concatenated motor assembly of claim 12, in which the seal assemblycooperates with the continuous rotatable shaft and communicates with thesecond motor module assembly.